1. Field
This invention relates generally to charge pump circuits, and more specifically to a charge pump circuit that has more than one type of operation.
2. Related Art
A charge pump circuit is used for supplying other circuits with a voltage at a value other than a value of a supply voltage. A charge pump circuit includes a charge pump, which is a circuit that produces a voltage that is higher or lower than its input voltage, and a regulation stage that regulates the voltage produced by the charge pump.
FIG. 1 is a block diagram of a simplified charge pump circuit 100, which includes an input terminal for receiving an input voltage VIN, an input terminal for receiving an ENABLE signal, an input terminal for receiving clock signals, an output terminal for outputting a PUMP_OK signal, and an output terminal for outputting an output voltage VOUT. An output capacitor Cout is coupled between the VOUT output terminal and a ground terminal. The charge pump circuit 100 includes a plurality of pump unit cells, or configurable pullup units (CPUC), one of which is illustrated in an idealized way in FIG. 1. Each pump unit cell includes a diode and a pump capacitor Ci.
FIG. 2 is a chart 200 showing signals in the charge pump circuit 100. The ENABLE signal activates the charge pump circuit 100. A charge pump circuit has basically three modes of operation: skip mode, linear mode and linskip mode, which is a combination of the other two modes. Regardless of the mode of operation of a charge pump circuit, VOUT of a charge pump circuit has a value of VIN when the charge pump circuit is first activated and VOUT increases in relatively small steps Vstep, each step occurring at intervals dependent upon a frequency of the clock signal. Therefore, VOUT needs a certain amount of time Δt to reach a target value VTARG. Circuits supplied with power from a charge pump circuit may need to wait such certain amount of time for VOUT to reach VTARG before being able to utilize the power from the charge pump circuit. In a charge pump circuit, Δt is basically dependent on capacity of the charge pump. The state of the PUMP_OK signal indicates that VOUT is stabilized at VTARG.
One known method of reducing Δt is to increase the clock frequency, but increasing the clock frequency can cause detrimental electromagnetic compatibility (EMC) and electromagnetic interference (EMI) effects. Another known method of reducing Δt is to increase the capacitance of each Ci, but increasing the capacitance of each Ci has a disadvantage of increasing the area of the charge pump. For example, doubling the capacitance of each Ci would almost double the area of the charge pump.